Stents are tubular support structures that are implanted into body vessels to treat blockages, occlusions, narrowing ailments and other problems that may restrict flow through the vessel. Numerous vessels throughout the vascular system, including peripheral arteries, such as the carotid, brachial, renal, iliac and femoral arteries, and other vessels, may benefit from treatment by a stent. Typically, stents are delivered into a vessel in a low-profile delivery configuration and then radially expanded at a treatment site to support the vessel wall. Balloon-expandable stents expand in response to the inflation of a balloon, whereas self-expanding stents deploy automatically when released from a delivery device.
Self-expanding stents are often fabricated from superelastic or shape memory alloys, such as Nitinol, which can “remember” and recover a previous shape. For example, a self-expanding stent may be engineered to remember and recover an expanded configuration after being delivered into a vessel in a compressed, low profile state. In the case of Nitinol alloys, the source of the shape recovery is generally understood to be a phase transformation between a lower temperature phase (martensite) and a higher temperature phase (austenite), which may be driven by an increase in temperature (shape memory effect) or by the removal of an applied stress (superelastic effect).